Add lxc-tor-relay build type with nyx monitoring

New tor-relay build type (currently lxc-only) running a plain Tor
middle relay via modules/tor/enable-relay.nix, plus nyx for
interactive monitoring over the relay's control socket.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

variables.nix

@@ -137,6 +137,14 @@
     # shortcuts on the gui build type (hosts/nixos/home.nix).
     pveWeb = 8006;
     pbsWeb = 8007;
+
+    # Tor relay's ORPort — the port other Tor relays connect to for onion
+    # routing traffic (modules/tor/enable-relay.nix). Tor's own conventional
+    # default; opened via services.tor.openFirewall rather than
+    # networking.firewall.allowedTCPPorts directly, but kept here anyway so
+    # it's not a bare literal duplicated between the relay's settings and
+    # anything else that ever needs to reference it.
+    torRelayOrPort = 9001;
   };
 
   # .raw disk image size for every proxmox-* host's standalone Disko image